1. Field of the Invention
This invention relates to a method for making a light emitting device, more particularly to a method for manufacturing a light emitting device involving application of a temporary element having a laser-transmissive substrate and a laser-dissociable layer.
2. Description of the Related Art
Since light emitting diodes have a relatively small size, they have been widely utilized in backlight modules, computers, traffic lights, and outdoor displays.
For a conventional blue light emitting diode, since blue light has a relatively wide energy gap and requires a relatively high exciting energy to bridge the energy gap, the driving current applied to the blue light emitting diode is correspondingly high. Accumulative heat will increase with an increase in current injected into the blue light emitting diode. Therefore, output power of the blue light emitting diode will be reduced due to failure of heat dissipation, and intensity of light emitted by the blue light emitting diode is not satisfactory, accordingly.
Attempts have been made to improve insufficient emitted light intensity of the blue light emitting diode through epitaxial process techniques, chip-processing techniques, and packaging techniques. For the epitaxial process techniques, it has been tried to increase concentrations of donors and acceptors in the light emitting layer, and to decrease dislocation density of the light emitting layer. Nevertheless, it is relatively difficult to increase the concentration of the acceptors in the light emitting layer, particularly in the light emitting layer of GaN system having a relatively wide energy gap. Since there is a relatively high degree of lattice mismatch between sapphire substrate and gallium nitride layer formed on the sapphire substrate in the conventional light emitting diode, it is difficult to make a breakthrough in reducing dislocation density of the active light emitting layer.
Referring to FIG. 1, a conventional blue light emitting diode 1 includes: a sapphire substrate 11 having a top surface 111, and a bottom surface 112 opposite to the top surface 111; a GaN epitaxial layer 12 formed on the top surface 111; a reflective layer 13 formed on the bottom surface 112; an adhesive layer 14 formed on the reflective layer 13; and a Si heat-dissipating substrate 15 attached to the reflective layer 13 through the adhesive layer 14.
The GaN epitaxial layer 12 includes a N-type semiconductor sub-layer 121 having a first region and a second region, a light emitting sub-layer 122 formed on the second region of the N-type semiconductor sub-layer 121, a P-type semiconductor sub-layer 123 formed on the light emitting sub-layer 122, and first and second electrodes 124, 125 formed on the first region of the N-type semiconductor sub-layer 12 and the P-type semiconductor sub-layer 123, respectively.
Particularly, the sapphire substrate 11 is thinned so as to have a thickness ranging from 80 μm to 100 μm.
However, commercially available sapphire substrates suitable for the conventional blue light emitting diode 1 have a relatively low conductivity, and a thickness ranging from 380 μm to 430 μm. Even though such sapphire substrates are thinned to 80 μm to 100 μm in thickness, when used in the blue light emitting diode 1, reduction of output power, which is attributed to excessive accumulative heat generated by a high current injected into the conventional light emitting diode 1, cannot be avoided. Output power of the conventional blue light emitting diode 1 is saturated when the injected current reaches about 75 mA. The output power of the conventional blue light emitting diode 1 cannot be further increased by increasing the current to more than 75 mA, which instead causes the output power to decrease due to excessive accumulative heat.
Therefore, there is still a need in the art to provide a method for improving heat dissipation of the light emitting diode, particularly the blue light emitting diode.